We demonstrated 40-Gbit/s operations of 1. 55-fom InGaAlAs multiple-quantum-well (MQW) electro-absorption (EA) modulators in wide temperature range from 0 to 85-C as a basic study of an uncooled EA/DFB (distributed feedback) laser, which is one of the most promising method to achieve a low-cost optical transmitter. When the wavelength of the input optical source is set to keep the detuning constant, a good dynamic extinction ratio (ER) of 8.5 dB was obtained even at high temperature, i.e., 65℃, and the dynamic ER degradation between 25 and 65℃ was only 1.6 dB. When the input optical wavelength is controlled to match the temperature sensitivity of a DFB laser, the dynamic ER was better than 7.8 dB hi the temperature range from 0 to 85℃ by adjusting the center-level voltage of the EA modulator. These results show that when our 40-Gbit/s EA modulator is monolithically integrated with a DFB laser, it can attain uncooled operations under wide temperature range from 0 to 85℃.